Of the approximately $1.5 billion spent
annually for termite control in the U.S., subterranean termites
account for an 80% share. Triple mark-recapture programs using
dye markers such as Sudan Red 7B Figure 1 revealed that a
single subterranean termite colony may contain millions of
foragers and may forage a distance of up to 300 ft (Su and
Scheffrahn 1988, Grace et al. 1989, Su et al. 1993). A large
subterranean termite colony, therefore, may inhabit large areas
of soil beneath an infested home Figure 2A. Conventional soil termiticides have been used for the
last four decades to provide a chemical barrier for the exclusion
of soil-borne termites from a structure Figure 2B. Typically, 100 - 200 gal. of liquid termiticide (8 -
17 lb. active ingredient @ 1% concentration) are applied in the
soil beneath and surrounding an infested home (NPCA 1985). The
vast proportion of subterranean termites, however, are not
affected by such soil termiticide treatment Figure 2B. These termites often find their way back into the
structure, causing costly re-treatment (Su and Scheffrahn 1988).

Population studies for field colonies of
subterranean termites indicated that wooden stakes placed near a
large colony of these cryptic insects are eventually attacked by
termites. Slow-acting and non-repellent toxicants may be
incorporated into such food sources to affect the vast population
of the subterranean termite colony (Su et al.1982) Figure 2C. Through an extensive laboratory screening program (Su
and Scheffrahn 1993), we discovered that a chitin synthesis
inhibitor, hexaflumuron, interfered with the molting process of
both the Formosan subterranean termite, Coptotermes formosanus,
and the eastern subterranean termite, Reticulitermes flavipes Figure 3. A baiting procedure that incorporated a matrix
containing hexaflumuron was evaluated against field colonies of
the Formosan and eastern subterranean termites (Su 1994a). Wooden
stakes were first driven into soil to detect the presence of
termites. Bait tubes were placed in the soil where termites were
detected. The results demonstrated that approximately 4 - 1,500
mg (less than 1/20 oz.) of hexaflumuron was needed for 90 - 100%
reduction of field populations containing 0.5 - 2.8 million
eastern subterranean termites per colony Figure 4, and 1.0 - 2.4 million Formosan subterranean termites
per colony Figure 5.
Elimination of colony populations created a zone of termite-free
soil surrounding a home for several years (Su 1994b).

Following the success of the initial field
trials, a prototype monitoring/baiting station was designed for
commercial application Figure 6. The station containing the monitoring device is first
installed in soil surrounding a home Figure 7A. When termites are found in the station Figure 7B, the monitoring device is replaced with a tube
containing bait laced with a minute amount of hexaflumuron Figure 7C. Termites collected from the monitoring device are
dislodged into an empty space on the top of the tube, called the
"recruiter's chamber." Figures 7C, D

Termites placed in the recruiter's chamber have
to feed their way out of the bait to reunite with nestmates Figures 8A, B. Left behind in the bait are their species- and
colony-specific odors Figure
8C. One of such chemicals is
the trail-following pheromone excreted from the sternal gland Figure 9, which guides nestmates to the bait. This
self-recruitment procedure enhances bait uptake by termites (Su
1994a). Hexaflumuron kills insects only when they molt every 1 -
2 months. During this period, the bait is thoroughly distributed
throughout the colony populations. The monitoring/baiting system
is currently commercialized under the Sentricon®
brand name by DowElanco (Indianapolis, IN), who invented and owns
the proprietary rights to hexaflumuron. Field trials using the
system typically require less than one gram (0.04 oz.) of
hexaflumuron to eliminate field populations of several million
termites (Su et al. 1995) Figure 10.